gma: Add a HW.PCI.Dev for dynamic MMIO setup

Remove `MMIO_Base` option from Initialize() and try to derive it
using libhwbase' PCI mechanism instead.

Change-Id: Iacd4d098954bb96c1c6b40fdfb2636191d9517c7
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/20600
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
diff --git a/common/hw-gfx-gma-config.ads.template b/common/hw-gfx-gma-config.ads.template
index dea26b8..b4e52f6 100644
--- a/common/hw-gfx-gma-config.ads.template
+++ b/common/hw-gfx-gma-config.ads.template
@@ -35,6 +35,8 @@
 
    ----------------------------------------------------------------------------
 
+   Default_MMIO_Base_Set   : constant Boolean := Default_MMIO_Base /= 0;
+
    Has_Internal_Display    : constant Boolean := Internal_Display /= None;
    Internal_Is_EDP         : constant Boolean := Internal_Display = DP;
    Has_Presence_Straps     : constant Boolean := CPU /= Broxton;